Dear fishliker,
becouse of tight space limits in todays mobile handsets, often active antnnas is using in them. more printed small dipoles, or ok, PIFA, but all ofem with very low gain (becouse of bad matching). so, if you really want to have the definition, you should looking for gain conditions in the operating band.
+the europian standard for mid-cell BTS antenna is S11<-15.